The example of a dog is very significant in this connection. A dog naturally does not become a devotee at any time, but still it is sometimes found that a dog of a devotee gradually becomes a devotee also. We have actually seen that a dog has no respect even for the tulasī plant. Indeed, a dog is especially inclined to pass urine on the tulasī plant. Therefore the dog is the number one non-devotee. But Śrī Caitanya Mahāprabhu’s saṅkīrtana movement is so strong that even a dog-like non-devotee can gradually become a devotee by the association of a devotee of Lord Caitanya. Śrīla Śivānanda Sena, a great householder devotee of Lord Caitanya Mahāprabhu, attracted a dog on the street while going to Jagannātha Purī. The dog began to follow him and ultimately went to see Caitanya Mahāprabhu and was liberated. Similarly, cats and dogs in the household of Śrīvāsa Ṭhākura were also liberated. Cats and dogs and other animals are not expected to become devotees, but in the association of a pure devotee they are also delivered.
Ref >> Srila Prabhupada Vani.